Over-coating agent for forming fine patterns and a method of forming fine patterns using such agent

ABSTRACT

It is disclosed an over-coating agent for forming fine patterns which is applied to cover a substrate having thereon photoresist patterns and allowed to shrink under heat so that the spacing between adjacent photoresist patterns is lessened, with the applied film of the over-coating agent being removed substantially completely to form or define fine trace patterns, further characterized by containing either a water-soluble polymer and an amide group-containing monomer or a water-soluble polymer which contains at least (meth)acrylamide as a monomeric component. Also disclosed is a method of forming fine-line patterns using any one of said over-coating agents. According to the invention, the thermal shrinkage of the over-coating agent for forming fine patterns in the heat treatment can be extensively increased, and one can obtain fine-line patterns which exhibit good profiles while satisfying the characteristics required of semiconductor devices.

TECHNICAL FIELD

This invention relates to an over-coating agent for forming finepatterns in the field of photolithographic technology and a method offorming fine-line patterns using such agent. More particularly, theinvention relates to an over-coating agent for forming or definingfine-line patterns, such as hole patterns and trench patterns, that canmeet today's requirements for higher packing densities and smaller sizesof semiconductor devices.

BACKGROUND ART

In the manufacture of electronic components such as semiconductordevices and liquid-crystal devices, there is employed thephotolithographic technology which, in order to perform a treatment suchas etching on the substrate, first forms a film (photoresist layer) overthe substrate using a so-called radiation-sensitive photoresist which issensitive to activating radiations, then performs exposure of the filmby selective illumination with an activating radiation, performsdevelopment to dissolve away the photoresist layer selectively to forman image pattern (photoresist pattern), and forms a variety of patternsincluding contact providing patterns such as hole patterns and trenchpatterns using the photoresist pattern as a protective layer (maskpattern).

With the recent increase in the need for higher packing densities andsmaller sizes of semiconductor devices, increasing efforts are beingmade to form sufficiently fine-line patterns and submicron-electronicfabrication capable of forming patterns with linewidths of no more than0.20 μm is currently required. As for the activating light raysnecessary in the formation of mask patterns, short-wavelength radiationssuch as KrF, ArF and F₂ excimer laser beams and electron beams areemployed. Further, active R&D efforts are being made to find photoresistmaterials as mask pattern formers that have physical properties adaptedto those short-wavelength radiations.

In addition to those approaches for realizing submicron-electronicfabrication which are based on photoresist materials, active R&D effortsare also being made on the basis of pattern forming method with a viewto finding a technology that can provide higher resolutions than thosepossessed by photoresist materials.

For example, JP-5-166717A discloses a method of forming fine patternswhich comprises the steps of defining patterns (=photoresist-uncoveredpatterns) into a pattern-forming resist on a substrate, then coatingover entirely the substrate with a mixing generating resist that is tobe mixed with said pattern-forming resist, baking the assembly to form amixing layer on both sidewalls and the top of the pattern-formingresist, and removing the non-mixing portions of said mixing generatingresist such that the feature size of the photoresist-uncovered patternis reduced by an amount comparable to the dimension of said mixinglayer. JP-5-241348A discloses a pattern forming method comprising thesteps of depositing a resin, which becomes insoluble in the presence ofan acid, on a substrate having formed thereon a resist patterncontaining an acid generator, heat treating the assembly so that theacid is diffused from the resist pattern into said resin insoluble inthe presence of an acid to form a given thickness of insolubilizedportion of the resist near the interface between the resin and theresist pattern, and developing the resist to remove the resin portionthrough which no acid has been diffused, thereby ensuring that thefeature size of the pattern is reduced by an amount comparable to thedimension of said given thickness.

However, in these methods, it is difficult to control the thickness oflayers to be formed on the sidewalls of resist patterns. In addition,the in-plane heat dependency of wafers is as great as ten-odd nanometersper degree Celsius, so it is extremely difficult to keep the in-planeuniformity of wafers by means of the heater employed in currentfabrication of semiconductor devices and this leads to the problem ofoccurrence of significant variations in pattern dimensions.

Another approach known to be capable of reducing pattern dimensions isby fluidizing resist patterns through heat treatment and the like. Forexample, JP-1-307228A discloses a method comprising the steps of forminga resist pattern on a substrate and applying heat treatment to deformthe cross-sectional shape of the resist pattern, thereby defining a finepattern. In addition, JP-4-364021A discloses a method comprising thesteps of forming a resist pattern and heating it to fluidize the resistpattern, thereby changing the dimensions of its resist pattern to formor define a fine-line pattern.

In these methods, the wafer's in-plane heat dependency is only a fewnanometers per degree Celsius and is not very problematic. On the otherhand, it is difficult to control the resist deformation and fluidizingon account of heat treatment, so it is not easy to provide a uniformresist pattern in a wafer's plane.

An evolved version of those methods is disclosed in JP-7-45510A and itcomprises the steps of forming a resist pattern on a substrate, forminga stopper resin on the substrate to prevent excessive thermal fluidizingof the resist pattern, then applying heat treatment to fluidize theresist so as t change the dimensions of its pattern, and thereafterremoving the stopper resin to form or define a fine-line pattern. As thestopper resin, a water-soluble resin, specifically, polyvinyl alcohol isemployed. However, polyvinyl alcohol is not highly soluble in water andcannot be readily removed completely by washing with water, introducingdifficulty in forming a pattern of good profile. The pattern formed isnot completely satisfactory in terms of stability over time. Inaddition, polyvinyl alcohol cannot be applied efficiently by coating.Because of these and other problems, the method disclosed in JP-7-45510Ahas yet to be adopted commercially.

JP 2001-281886A discloses a method comprising the steps of covering asurface of a resist pattern with an acidic film made of a resist patternsize reducing material containing a water-soluble resin, rendering thesurface layer of the resist pattern alkali-soluble, then removing saidsurface layer and the acidic film with an alkaline solution to reducethe feature size of the resist pattern. JP-2002-184673A discloses amethod comprising the steps of forming a resist pattern on a substrate,then forming a film containing a water-soluble film forming component onsaid resist pattern, heat treating said resist pattern and film, andimmersing the assembly in an aqueous solution of tetramethylammoniumhydroxide, thereby forming a fine-line resist pattern without involvinga dry etching step. However, both methods are simply directed toreducing the size of resist trace patterns themselves and therefore aretotally different from the present invention in object.

DISCLOSURE OF INVENTION

An object of the present invention is to provide an over-coating agentfor forming fine patterns. It can remarkably increase the thermalshrinkage of the over-coating agent in the heat treatment, thereby toform finer patterns effectively, and has high ability to control patterndimensions and provides fine-line patterns that have a satisfactorypro-file and satisfy the characteristics required of semiconductordevices. Another object of the invention is to provide a method offorming fine trace patterns using the over-coating agent.

In order to attain the first object, the present invention provides anover-coating agent for forming fine patterns which is applied to cover asubstrate having photoresist patterns thereon and allowed to shrinkunder heat so that the spacing between adjacent photoresist patterns islessened, with the applied film of the over-coating agent being removedsubstantially completely to form fine patterns, further characterized bycontaining either (i) a water-soluble polymer and an amidegroup-containing monomer, or (ii) a water-soluble polymer which containsat least (meth)acrylamide as its monomeric components.

In order to attain the second object, the present invention provides amethod of forming fine patterns comprising the steps of covering asubstrate having thereon photoresist patterns with either of theabove-described over-coating agent for forming fine patterns, thenapplying heat treatment to shrink the applied over-coating agent underthe action of heat so that the spacing between the adjacent photoresistpatterns is lessened, and subsequently completely removing the appliedfilm of the over-coating agent.

In a preferred embodiment, the heat treatment is performed by heatingthe assembly at a temperature that does not cause thermal fluidizing ofthe photoresist patterns on the substrate.

BEST MODE FOR CARRYING OUT THE INVENTION

The over-coating agent of the invention for forming fine features ofpatterns is used to be applied to cover a substrate, having photoresistpatterns (mask patterns) thereon, including patterns typified by holepatterns or trench patterns, each of these patterns are defined byspacing between adjacent photoresist patterns (mask patterns). Uponheating, the applied film of over-coating agent shrinks to increase thewidth of each of the photoresist patterns, thereby narrowing orlessening adjacent hole patterns or trench patterns as defined byspacing between the photoresist patterns and, thereafter, the appliedfilm is removed substantially completely to form or define finepatterns.

The phrase “removing the applied film substantially completely” as usedherein means that after lessening the spacing between adjacentphotoresist patterns by the heat shrinking action of the appliedover-coating agent, said film is removed in such a way that nosignificant thickness of the over-coating agent will remain at theinterface with the photoresist patterns. Therefore, the presentinvention does not include methods in which a certain thickness of theover-coating agent is left intact near the interface with thephotoresist pattern so that the feature size of the pattern is reducedby an amount corresponding to the residual thickness of the over-coatingagent.

The over-coating agent for forming fine patterns of the invention forforming fine patterns is what either comprising a water-soluble polymerand an amide-group containing monomer (first type of the over-coatingagent for forming fine patterns), or comprising a water-soluble polymerwhich contains at least (meth)acrylamide as its monomeric components(second type of the over-coating agent for forming fine patterns).

[First Type of the Over-Coating Agent for Forming Fine Patterns]Water-Soluble Polymer

The water-soluble polymer may be any polymer that can dissolve in waterat room temperature and various types may be employed without particularlimitation; preferred examples include acrylic polymers, vinyl polymers,cellulosic derivatives, alkylene glycol polymers, urea polymers,melamine polymers, epoxy polymers and amide polymers.

Exemplary acrylic polymers include polymers and copolymers havingmonomeric components, such as acrylic acid, methyl acrylate, methacrylicacid, methyl methacrylate, N,N-dimethylaminoethyl methacrylate,N,N-diethylaminoethyl methacrylate, N,N-dimethylaminoethyl acrylate,acryloylmorpholine, etc.

Exemplary vinyl polymers include polymers and copolymers havingmonomeric components, such as N-vinylpyrrolidone, vinyl imidazolidinone,vinyl acetate, etc.

Exemplary cellulosic derivatives include hydroxypropylmethyl cellulosephthalate, hydroxypropylmethyl cellulose acetate phthalate,hydroxypropylmethyl cellulose hexahydrophthalate, hydroxypropylmethylcellulose acetate succinate, hydroxypropylmethyl cellulose,hydroxypropyl cellulose, hydroxyethyl cellulose, cellulose acetatehexahydrophthalate, carboxymethyl cellulose, ethyl cellulose,methylcellulose, etc.

Exemplary alkylene glycol polymers include addition polymers andcopolymers of ethylene glycol, propylene glycol, etc.

Exemplary urea polymers include those having methyllolurea,dimethylolurea, ethyleneurea, etc. as components.

Exemplary melamine polymers include those having methoxymethylatedmelamine, methoxymethylated isobutoxymethylated melamine,methoxyethylated melamine, etc. as components.

Among epoxy polymers and amide polymers, those which are water-solublemay also be employed.

It is particularly preferred to employ at least one member selected fromthe group consisting of alkylene glycol polymers, cellulosicderivatives, vinyl polymers and acrylic polymers. Acrylic polymers aremost preferred since they provide ease in pH adjustment. Copolymerscomprising acrylic polymers and water-soluble polymers other thanacrylic polymers are also preferred since during heat treatment, theefficiency of shrinking the spacing between the adjacent photoresistpatterns (mask patterns) can be increased while maintaining the shape ofthe photoresist pattern. The water-soluble polymers can be employedeither singly or in combination.

When water-soluble polymers are used as copolymers, the proportions ofthe components are not limited to any particular values. However, ifstability over time is important, the proportion of the acrylic polymeris preferably adjusted to be larger than those of other buildingpolymers. Other than by using excessive amounts of the acrylic polymer,better stability over time can also be obtained by adding acidiccompounds such as p-toluenesulfonic acid and dodecylbenzenesulfonicacid.

Amide Group-Containing Monomer

The amide group-containing monomer should have characteristics such thatwhen added to the water-soluble polymer, it is highly soluble, is notsuspended, and is compatible with the polymer component.

As the amide group-containing monomer, preferred one is an amidecompound represented by the following general formula (I):

where R₁ is a hydrogen atom, an alkyl or hydroxyalkyl group having 1-5carbon atoms; R₂ is an alkyl group having 1-5 carbon atoms; R₃ is ahydrogen atom or a methyl group; and m is a number of 0-5. The alkylgroup and the hydroxyalkyl group may be either linear of branched.

The amide group-containing monomer of the general formula (I) is morepreferred in which R₁ is a hydrogen atom, a methyl group or an ethylgroup, and m is 0. Specific examples of the amide group-containingmonomer include acrylamide, methacrylamide, N,N-dimethylacrylamide,N,N-dimethylmethacrylamide, N,N-diethylacrylamide,N,N-diethylmethacrylamide, N-methylacrylamide, N-methylmethacrylamide,N-ethylacrylamide and N-ethylmethacrylamide. Among these, acrylamide andmethacrylamide are particularly preferred.

In the invention, the thermal shrinkage of the over-coating agent forforming fine patterns can be remarkably increased by the incorporationof the amide group-containing monomer, and thereby finer patterns can beformed.

The content of the amide group-containing monomer added is preferablyabout 0.1-30 mass, and particularly about 1-15 mass, based on theover-coating agent for forming fine patterns (solid content). In thecase where the content is less than 0.1 mass, a large thermal shrinkagecannot be obtained of the over-coating agent for forming fine patterns.However, in the case where the content exceeds 30 mass, there is noappreciable improvement in the thermal shrinkage that justifies theincreased content.

[Second Type of the Over-Coating Agent for Forming Fine Patterns]

In one preferred embodiment in the second type of the over-coating agentof the invention, a water-soluble polymer is a copolymer of(meth)acrylamide and at least one member selected from among monomericcomponents of alkylene glycol polymers, cellulosic derivatives, vinylpolymers, acrylic polymers, urea polymers, epoxy polymers and melaminepolymers, provided that monomeric components of acrylic polymers arethose other than (meth)acrylamide).

Exemplary monomeric components of acrylic polymers include acrylic acid,methyl acrylate, methacrylic acid, methyl methacrylate,N,N-dimethylaminoethyl methacrylate, N,N-diethylaminoethyl methacrylate,N,N-dimethylaminoethyl acrylate, acryloylmorpholine, etc.

Exemplary monomeric components of vinyl polymers includeN-vinylpyrrolidone, vinyl imidazolidinone, vinyl acetate, etc.

Exemplary monomeric components of cellulosic derivatives includehydroxypropylmethyl cellulose phthalate, hydroxypropylmethyl celluloseacetate phthalate, hydroxypropylmethyl cellulose hexahydrophthalate,hydroxypropylmethyl cellulose acetate succinate, hydroxypropylmethylcellulose, hydroxypropyl cellulose, hydroxyethyl cellulose, celluloseacetate hexahydrophthalate, carboxymethyl cellulose, ethyl cellulose,methylcellulose, etc.

Exemplary monomeric components of alkylene glycol polymers includeethylene glycol, propylene glycol, etc.

Exemplary monomeric components of urea polymers include methylolurea,dimethylolurea, ethyleneurea, etc.

Exemplary monomeric components of melamine polymers includemethoxymethylated melamine, methoxymethylated isobutoxymethylatedmelamine, methoxyethylated melamine, etc.

Among monomeric components of epoxy polymers, those which arewater-soluble may also be employed.

It is particularly preferred to employ monomeric components of acrylicpolymers, specifically (meth)acrylic acid, are most preferred sinceduring heat treatment, the efficiency of shrinking the spacing betweenthe adjacent photoresist patterns can be extensively increased whilemaintaining the shape of the photoresist pattern. They are alsopreferred in terms of stability over time.

Copolymers of (meth)acrylamide and the monomeric components of theabove-described polymers are preferably used in which the monomers areused in an amount of 0.1-30 mass %, more preferably about 1-15 mass %,relative to (meth) acrylamide.

In another preferred embodiment in the second type of the over-coatingagent of the invention, a water-soluble polymer is a copolymer or amixture of (meth)acrylamide and at least one member selected from amongpolymers of alkylene glycol polymers, cellulosic derivatives, vinylpolymers, acrylic polymers (with the exception of poly(meth)acrylamide),urea polymers, epoxy polymers and melamine polymers.

Alkylene glycol polymers, cellulosic derivatives, vinyl polymers,acrylic polymers, urea polymers, epoxy polymers and melamine polymersare preferably used the same ones having monomeric components asdescried above.

Among them, acrylic polymers, particularly poly(meth)acrylate, such aspoly(meth)acrylic acid, are most preferred since during heat treatment,the efficiency of shrinking the spacing between the adjacent photoresistpatterns (mask patterns) can be extensively increased while maintainingthe shape of the photoresist pattern. It is also preferred in terms ofstability over time.

Copolymers or mixed resins of (meth)acrylamide and each of the abovepolymers are preferably used in which the copolymers are used in anamount of 0.1-30 mass %, more preferably about 1-15 mass, relative to(meth)acrylamide.

In either of the two embodiments above, it is also possible to improvethe stability over time by adding an acidic compound such asp-toluenesulfonic acid or dodecylbenzenesulfonic acid.

Optional Additives

In the first and second types of over-coating agent for forming finepatters may additionally contain water-soluble amines for specialpurposes such as preventing the generation of impurities and pHadjustment.

Exemplary water-soluble amines include amines having pKa (aciddissociation constant) values of 7.5-13 in aqueous solution at 25° C.Specific examples include the following: alkanolamines, such asmonoethanolamine, diethanolamine, triethanolamine,2-(2-aminoethoxy)ethanol, N,N-dimethylethanolamine,N,N-diethylethanolamine, N,N-dibutylethanolamine, N-methylethanolamine,N-ethylethanolamine, N-butylethanolamine, N-methyldiethanolamine,monoisopropanolamine, diisopropanolamine and triisopropanolamine;polyalkylenepolyamines, such as diethylenetriamine,triethylenetetramine, propylenediamine, N,N-diethylethylenediamine,1,4-butanediamine, N-ethylethylenediamine, 1,2-propanediamine,1,3-propanediamine and 1,6-hexanediamine; aliphatic amines, such as2-ethylhexylamine, dioctylamine, tributylamine, tripropylamine,triallylamine, heptylamine and cyclohexylamine; aromatic amines, such asbenzylamine and diphenylamine; and cyclic amines, such as piperazine,N-methyl-piperazine and hydroxyethylpiperazine. Preferred water-solubleamines are those having boiling points of 140° C. (760 mmHg), asexemplified by monoethanolamine and triethanolamine.

If the water-soluble amine is to be added, it is preferably incorporatedin an amount of about 0.1-30 mass %, more preferably about 2-15 mass %,of the over-coating agent for forming fine patterns (in terms of solidscontent). If the water-soluble amine is incorporated in an amount ofless than 0.1 mass %, the coating fluid may deteriorate over time. Ifthe water-soluble amine is incorporated in an amount exceeding 30 mass%, the photoresist pattern being formed may deteriorate in shape.

For such purposes as reducing the dimensions of patterns and controllingthe occurrence of defects, the first and second types of over-coatingagent for forming fine patterns may further optionally contain non-aminebased, water-soluble organic solvents.

As such non-amine based, water-soluble organic solvents, any non-aminebased organic solvents that can mix with water may be employed and theymay be exemplified by the following: sulfoxides, such as dimethylsulfoxide; sulfones, such as dimethylsulfone, diethylsulfone,bis(2-hydroxyethyl)sulfone and tetramethylenesulfone; amides, such asN,N-dimethylformamide, N-methylformamide, N,N-dimethylacetamide,N-methylacetamine and N,N-diethylacetamide; lactams, such asN-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N-propyl-2-pyrrolidone,N-hydroxymethyl-2-pyrrolidone and N-hydroxyethyl-2-pyrrolidone;imidazolidinones, such as 1,3-dimethyl-2-imidazolidinone,1,3-diethyl-2-imidazolidinone and 1,3-diisopropyl-2-imidazolidinone; andpolyhydric alcohols and derivatives thereof, such as ethylene glycol,ethylene glycol monomethyl ether, ethylene glycol monoethyl ether,ethylene glycol monobuthyl ether, ethylene glycol monomethyl etheracetate, ethylene glycol monoethyl ether acetate, diethylene glycol,diethylene glycol monomethyl ether, diethylene glycol monoethyl ether,diethylene glycol monobuthyl ether, propylene glycol, propylene glycolmonomethyl ether, glycerol, 1,2-butylene glycol, 1,3-butylene glycol and2,3-butylene glycol. Among those mentioned above, polyhydric alcoholsand their derivatives are preferred for the purposes of reducing thedimensions of patterns and controlling the occurrence of defects andglycerol is particularly preferred. The non-amine based, water-solubleorganic solvents may be used either singly or in combination.

If the non-amine based, water-soluble organic solvent is to be added, itis preferably incorporated in an amount of about 0.1-30 mass %, morepreferably about 0.5-15 mass %, of the water-soluble polymer. If thenon-amine based, water-soluble organic solvent is incorporated in anamount of less than 0.1 mass %, its defect reducing effect tends todecrease. Beyond 30 mass %, a mixing layer is liable to form at theinterface with the photoresist pattern.

In addition, the first and second type of over-coating agent mayoptionally contain a surfactant for attaining special effects such ascoating uniformity and wafer's in-plane uniformity.

Suitable surfactants include N-alkylpyrrolidones, quaternary ammoniumsalts and phosphate esters of polyoxyethylene.

N-alkylpyrrolidones as surfactant are preferably represented by thefollowing general formula (II):

where R₄ is an alkyl group having at least 6 carbon atoms.

Specific examples of N-alkylpyrrolidones as surfactant includeN-hexyl-2-pyrrolidone, N-heptyl-2-pyrrolidone, N-octyl-2-pyrrolidone,N-nonyl-2-pyrrolidone, N-decyl-2-pyrrolidone, N-undecyl-2-pyrrolidone,N-dodecyl-2-pyrrolidone, N-tridecyl-2-pyrrolidone,N-tetradecyl-2-pyrrolidone, N-pentadecyl-2-pyrrolidone,N-hexadecyl-2-pyrrolidone, N-heptadecyl-2-pyrrolidone andN-octadecyl-2-pyrrolidone. Among these, N-octyl-2-pyrrolidone(“SURFADONE LP 100” of ISP Inc.) is preferably used.

Quaternary ammonium salts as surfactant are preferably represented bythe following general formula (III):

where R₅, R₆, R₇ and R₈ are each independently an alkyl group or ahydroxyalkyl group (provided that at least one of them is an alkyl orhydroxyalkyl group having not less than 6 carbon atoms); X⁻ is ahydroxide ion or a halogenide ion.

Specific examples of quaternary ammonium salts as surfactant includedodecyltrimethylammonium hydroxide, tridecyl-trimethylammoniumhydroxide, tetradecyltrimethylammonium hydroxide,pentadecyltrimethylammonium hydroxide, hexadecyltrimethylammoniumhydroxide, heptadecyltrimethylammonium hydroxide andoctadecyltrimethylammonium hydroxide. Among these,hexadecyltrimethylammonium hydroxide is preferably used.

Phosphate esters of polyoxyethylene are preferably represented by thefollowing general formula (IV):

where R₉ is an alkyl or alkylaryl group having 1-10 carbon atoms; R₁₀ isa hydrogen atom or (CH₂CH₂O)R₉ (where R₉ is as defined above); n is aninteger of 1-20.

To mention specific examples, phosphate esters of polyoxyethylene thatcan be used as surfactants are commercially available under trade names“PLYSURF A212E” and “PLYSURF A210G” from Dai-ichi Kogyo Seiyaku Co.,Ltd.

The first and second types of over-coating agent of the invention forforming fine patterns are preferably used as an aqueous solution at aconcentration of 3-50 mass %, more preferably at 5-30 mass %. If theconcentration of the aqueous solution is less than 3 mass %, poorcoverage of the substrate may result. If the concentration of theaqueous solution exceeds 50 mass %, there is no appreciable improvementin the intended effect that justifies the increased concentration andthe solution cannot be handled efficiently.

As already mentioned, the first and second types of over-coating agentof the invention for forming fine patterns are usually employed as anaqueous solution using water as the solvent. A mixed solvent systemcomprising water and an alcoholic solvent may also be employed.Exemplary alcoholic solvents are monohydric alcohols including methylalcohol, ethyl alcohol, propyl alcohol and isopropyl alcohol. Thesealcoholic solvents are mixed with water in amounts not exceeding about30 mass %.

The first and second types of over-coating agent of the invention forforming fine patterns have the advantage of improving resolution beyondthe values inherent in photoresist materials and it can attain wafer'sin-plane uniformity by eliminating the pattern variations in the planeof the substrate. Further, the over-coating agent of the invention canform patterns of good profile by eliminating the irregularities(roughness) in the shape of patterns due, for example, to the reflectionof fluorescent light from the substrate. Also it has remarkableimprovement in forming finer patterns.

The method of forming fine-line patterns according to the second aspectof the invention comprises the steps of covering a substrate havingphotoresist patterns thereon with either of the first and second typesof the above-described over-coating agent for forming fine patterns,then applying heat treatment to shrink the applied over-coating agentunder the action of heat so that the spacing between the adjacentphotoresist patterns is reduced, and subsequently removing the appliedfilm of the over-coating agent substantially completely.

The method of preparing the substrate having photoresist patternsthereon is not limited to any particular type and it can be prepared byconventional methods employed in the fabrication of semiconductordevices, liquid-crystal display devices, magnetic heads and microlensarrays. In an exemplary method, a photoresist composition of chemicallyamplifiable or other type is spin- or otherwise coated on a substratesuch as a silicon wafer and dried to form a photoresist layer, which isilluminated with an activating radiation such as ultraviolet,deep-ultraviolet or excimer laser light through a desired mask patternusing a reduction-projection exposure system or subjected to electronbeam photolithography, then heated and developed with a developer suchas an alkaline aqueous solution, typically a 1-10 mass %tetramethylammonium hydroxide (TMAH) aqueous solution, thereby forming aphotoresist pattern on the substrate.

The photoresist composition serving as a material from which photoresistpatterns are formed is not limited in any particular way and any commonphotoresist compositions may be employed including those for exposure toi- or g-lines, those for exposure with an excimer laser (e.g. KrF, ArFor F₂) and those for exposure to EB (electron beams).

[a.] Over-Coating Agent Application Step

After thusly forming the photoresist pattern as a mask pattern, theover-coating agent for forming fine patterns is applied to coverentirely the substrate. After applying the over-coating agent, thesubstrate may optionally be pre-baked at a temperature of 80-100° C. for30-90 seconds.

The over-coating agent may be applied by any methods commonly employedin the conventional heat flow process. Specifically, an aqueous solutionof the over-coating agent for forming fine patterns is applied to thesubstrate by any known application methods including whirl coating witha spinner, etc.

[b.] Heat Treatment (Thermal Shrinkage) Step

In the next step, heat treatment is performed to cause thermal shrinkageof the film of the over-coating agent. Under the resulting force ofthermal shrinkage of the film, the dimensions of the photoresist patternin contact with the film will increase by an amount equivalent to thethermal shrinkage of the film and, as the result, the photoresistpattern widens and accordingly the spacing between the adjacentphotoresist patterns lessens. The spacing between the adjacentphotoresist patterns determines the diameter or width of the patterns tobe finally obtained, so the decrease in the spacing between the adjacentphotoresist patterns contributes to reducing the diameter of eachelement of hole patterns or the width of each element of trenchpatterns, eventually leading to the definition of a pattern with smallerfeature sizes.

The heating temperature is not limited to any particular value as longas it is high enough to cause thermal shrinkage of the film of theover-coating agent and form or define a fine pattern. Heating ispreferably done at a temperature that will not cause thermal fluidizingof the photoresist pattern. The temperature that will not cause thermalfluidizing of the photoresist pattern is such a temperature that when asubstrate on which the photoresist pattern has been formed but no filmof the over-coating agent has been formed is heated, the photoresistpattern will not experience any dimensional changes (for example,dimensional changes due to spontaneously fluidized deforming).Performing a heat treatment under such temperature conditions is veryeffective for various reasons, e.g. a fine-line pattern of good profilecan be formed more efficiently and the duty ratio in the plane of awafer, or the dependency on the spacing between photoresist patterns inthe plane of a wafer, can be reduced.

Considering the softening points of a variety of photoresistcompositions employed in current photolithographic techniques, thepreferred heat treatment is usually performed within a temperature rangeof about 80-160° C. for 30-90 seconds, provided that the temperature isnot high enough to cause thermal fluidizing of the photoresist.

The thickness of the film of the over-coating agent for the formation offine-line patterns is preferably just comparable to the height of thephotoresist pattern or high enough to cover it.

[c.] Over-Coating Agent Removal Step

In the subsequent step, the remaining film of the over-coating agent onthe patterns is removed by washing with an aqueous solvent, preferablypure water, for 10-60 seconds. Prior to washing with water, rinsing mayoptionally be performed with an aqueous solution of alkali (e.g.tetramethylammonium hydroxide (TMAH) or choline). The over-coating agentof the present invention is easy to remove by washing with water and itcan be completely removed from the substrate and the photoresistpattern.

As a result, each pattern on the substrate has a smaller feature sizebecause each pattern is defined by the narrowed spacing between theadjacent widened photoresist patterns.

The fine-line pattern thus formed using the over-coating agent of thepresent invention has a pattern size smaller than the resolution limitattainable by the conventional methods. In addition, it has a goodenough profile and physical properties that can fully satisfy thecharacteristics required of semiconductor devices.

Steps [a.]-[c.] may be repeated several times. By repeating steps[a.]-[c.] several times, the photoresist trace patterns (mask patterns)can be progressively widened. The over-coating agent of the inventioncontains a water-soluble polymer and an amide group-containing monomer,so even if it is subjected to a plurality of washing steps, it can becompletely removed each time it is washed with water. Consequently, evenin the case of using a substrate having a thick film of photoresistpattern, a fine-line pattern of good profile can be formed on thesubstrate without causing pattern distortion or deformation.

The technical field of the present invention is not limited to thesemiconductor industry and it can be employed in a wide range ofapplications including the fabrication of liquid-crystal displaydevices, the production of magnetic heads and even the manufacture ofmicrolens arrays.

EXAMPLES

The following examples are provided for further illustrating the presentinvention but are in no way to be taken as limiting. Unless otherwisenoted, all amounts of ingredients are expressed in mass.

[First Type of the Over-Coating Agent for Forming Fine Patterns] Example1

A copolymer of acrylic acid and vinylpyrrolidone [5.83 g; acrylicacid/vinylpyrrolidone=2:1 (polymerization ratio)], triethanolamine (0.53g), acrylamide (0.58 g) and “PLYSURF A210G”, product of Dai-ichi KogyoSeiyaku Co., as phosphate esters of polyoxyethylene surfactant (0.06 g)were dissolved in water (93 g) to prepare an over-coating agent.

A substrate was whirl coated with a positive-acting photoresistTArF-7a-52 EM (product of Tokyo Ohka Kogyo Co., Ltd.), and baked at 115°C. for 90 seconds to form a photoresist layer in a thickness of 0.40 μm.

The photoresist layer was exposed with a laser exposure unit (NikonS-302 of Nikon Corp.), subjected to heat treatment at 100° C. for 90seconds and developed with an aqueous solution of 2.38 mass % TMAH(tetramethylammonium hydroxide) to form photoresist patterns whichdefined hole patterns with an each diameter of 161.0 nm.

Then above-described over-coating agent was applied onto the substrateincluding the hole patterns and subjected to heat treatment at 150° C.for 60 seconds. Subsequently, the over-coating agent was removed usingpure water at 23° C. The each diameter of the hole patterns was reducedto 122.0 nm.

Example 2

A copolymer of acrylic acid and vinylpyrrolidone [6.14 g; acrylicacid/vinylpyrrolidone=2:1 (polymerization ratio)], glycerol (0.18 g),acrylamide (0.62 g) and “PLYSURF A210G”, product of Dai-ichi KogyoSeiyaku Co., as phosphate esters of polyoxyethylene surfactant (0.06 g)were dissolved in water (93 g) to prepare an over-coating agent.

Then above-described over-coating agent was applied onto the substrateincluding the hole patterns (each diameter of patterns: 161.0 nm) whichwas prepared in the same manner as described in EXAMPLE 1, and subjectedto heat treatment at 150° C. for 60 seconds. Subsequently, theover-coating agent was removed using pure water at 23° C. The eachdiameter of the hole patterns was reduced to 121.7 nm.

Example 3

A copolymer of acrylic acid and vinylpyrrolidone [6.14 g; acrylicacid/vinylpyrrolidone=2:1 (polymerization ratio)], glycerol (0.18 g),methacrylamide (0.62 g) and “PLYSURF A210G”, product of Dai-ichi KogyoSeiyaku Co., as phosphate esters of polyoxyethylene surfactant (0.06 g)were dissolved in water (93 g) to prepare an over-coating agent.

Then above-described over-coating agent was applied onto the substrateincluding the hole patterns (each diameter of patterns: 161.0 nm) whichwas prepared in the same manner as described in EXAMPLE 1, and subjectedto heat treatment at 150° C. for 60 seconds. Subsequently, theover-coating agent was removed using pure water at 23° C. The eachdiameter of the hole patterns was reduced to 122.6 nm.

[Second Type of the Over-Coating Agent for Forming Fine Patterns]Example 4

A copolymer of acrylamide and acrylic acid [6.37 g; acrylamide/acrylicacid=1:2 (polymerization ratio)], triethanolamine (0.57 g) and “PLYSURFA210G”, product of Daiichi Kogyo Seiyaku Co., as phosphate esters ofpolyoxyethylene surfactant (0.06 g) were dissolved in water (93 g) toprepare an over-coating agent.

Then above-described over-coating agent was applied onto the substrateincluding the hole patterns (each diameter of patterns: 161.0 nm) whichwas prepared in the same manner as described in EXAMPLE 1, and subjectedto heat treatment at 150° C. for 60 seconds. Subsequently, theover-coating agent was removed using pure water at 23° C. The eachdiameter of the hole patterns was reduced to 121.8 nm.

Example 5

A mixed resin of polyacrylamide and polyacrylate [6.40 g;polyacrylamide/polyacrylate=1:2 (mass ratio)], triethanolamine (0.54 g)and “PLYSURF A210G”, product of Dai-ichi Kogyo Seiyaku Co., as phosphateesters of polyoxyethylene surfactant (0.06 g) were dissolved in water(93 g) to prepare an over-coating agent.

Then above-described over-coating agent was applied onto the substrateincluding the hole patterns (each diameter of patterns: 161.0 nm) whichwas prepared in the same manner as described in EXAMPLE 1, and subjectedto heat treatment at 150° C. for 60 seconds. Subsequently, theover-coating agent was removed using pure water at 23° C. The eachdiameter of the hole patterns was reduced to 123.0 nm.

COMPARATIVE EXAMPLE 1

A copolymer of acrylic acid and vinylpyrrolidone [5.83 g; acrylicacid/vinylpyrrolidone=2:1 (polymerization ratio)], triethanolamine (0.53g) and “PLYSURF A210G”, product of Dai-ichi Kogyo Seiyaku Co., asphosphate esters of polyoxyethylene surfactant (0.06 g) were dissolvedin water (93.58 g) to prepare an over-coating agent.

Then above-described over-coating agent was applied onto the substrateincluding the hole patterns (each diameter of patterns: 161.0 nm) whichwas prepared in the same manner as described in EXAMPLE 1, and subjectedto heat treatment at 150° C. for 60 seconds. Subsequently, theover-coating agent was removed using pure water at 23° C. The eachdiameter of the hole patterns was 139.0 nm.

COMPARATIVE EXAMPLE 2

A copolymer of acrylic acid and vinylpyrrolidone [6.73 g; acrylicacid/vinylpyrrolidone=2:1 (polymerization ratio)], glycerol (0.20 g) and“PLYSURF A210G”, product of Daiichi Kogyo Seiyaku Co., as phosphateesters of polyoxyethylene surfactant (0.07 g) were dissolved in water(93 g) to prepare an over-coating agent.

Then above-described over-coating agent was applied onto the substrateincluding the hole patterns (each diameter of patterns: 161.0 nm) whichwas prepared in the same manner as described in EXAMPLE 1, and subjectedto heat treatment at 150° C. for 60 seconds. Subsequently, theover-coating agent was removed using pure water at 23° C. The eachdiameter of the hole patterns was 140.6 nm.

INDUSTRIAL APPLICABILITY

As described above in detail, according to the present inventions of theover-coating agent for forming fine-line patterns and the method offorming fine-line patterns using the agent, the thermal shrinkage of theover-coating agent in the heat treatment can be extensively increased,and one can obtain fine-line patterns which exhibit good profiles whilesatisfying the characteristics required of semiconductor devices.

1. An over-coating agent for forming fine patterns which is applied tocover a substrate having photoresist patterns thereon and allowed toshrink under heat so that the spacing between adjacent photoresistpatterns is lessened, with the applied film of the over-coating agentbeing removed substantially completely to form fine patterns, furthercharacterized by containing a water-soluble polymer and an amidegroup-containing monomer.
 2. The over-coating agent for forming finepatterns according to claim 1, wherein the amide group-containingmonomer is an amide compound which is represented by the general formula(I):

where R₁ is a hydrogen atom, an alkyl or hydroxyalkyl group having 1-5carbon atoms; R₂ is an alkyl group having 1-5 carbon atoms; R₃ is ahydrogen atom or a methyl group; and m is a number of 0-5.
 3. Theover-coating agent for forming fine patterns according to claim 2,wherein in the general formula (I), R₁ is a hydrogen atom, a methylgroup or an ethyl group; and m is
 0. 4. The over-coating agent forforming fine patterns according to claim 1, wherein the amidegroup-containing monomer is acrylamide and/or methacrylamide.
 5. Theover-coating agent for forming fine patterns according to claim 1, whichcontains 0.1-30 mass % of the amide group-containing monomer in theover-coating agent (as solids).
 6. The over-coating agent for formingfine patterns according to claim 1, wherein the water-soluble polymer isat least one member selected from the group consisting of alkyleneglycolic polymers, cellulosic derivatives, vinyl polymers, acrylicpolymers, urea polymers, epoxy polymers, melamine polymers and amidepolymers.
 7. The over-coating agent for forming fine patterns accordingto claim 1, wherein the water-soluble polymer is at least one memberselected from the group consisting of alkylene glycolic polymers,cellulosic derivatives, vinyl polymers and acrylic polymers.
 8. Anover-coating agent for forming fine patterns which is applied to cover asubstrate having photoresist patterns thereon and allowed to shrinkunder heat so that the spacing between adjacent photoresist patterns islessened, with the applied film of the over-coating agent being removedsubstantially completely to form fine patterns, further characterized bycontaining a water-soluble polymer which contains at least(meth)acrylamide as its monomeric component.
 9. The over-coating agentfor forming fine patterns according to claim 8, wherein thewater-soluble polymer is a copolymer of (meth)acrylamide and at leastone member selected from among monomeric components of alkylene glycolicpolymers, cellulosic derivatives, vinyl polymers, acrylic polymers, ureapolymers, epoxy polymers and melamine polymers, with the proviso thatmonomeric components of acrylic polymers are those other than(meth)acrylamide.
 10. The over-coating agent for forming fine patternsaccording to claim 8, wherein the water-soluble polymer is a copolymeror a mixture of (meth)acrylamide and at least one member of polymersselected from the group consisting of alkylene glycolic polymers,cellulosic derivatives, vinyl polymers, acrylic polymers (with theexception of poly(meth)acrylamide), urea polymers, epoxy polymers andmelamine polymers.
 11. The over-coating agent for forming fine patternsaccording to claim 8, wherein the water-soluble polymer is a copolymerof (meth)acrylamide and at least one member selected from amongmonomeric components of acrylic polymers.
 12. The over-coating agent forforming fine patterns according to claim 8, wherein the water-solublepolymer is a copolymer or a mixture of poly(meth)acrylamide and acrylicpolymers.
 13. The over-coating agent for forming fine patterns accordingto claim 9, wherein the monomeric component of acrylic polymers is(meth)acrylic acid.
 14. The over-coating agent for forming fine patternsaccording to claim 11, wherein the monomeric component of acrylicpolymers is (meth)acrylic acid.
 15. The over-coating agent for formingfine patterns according to claim 10, wherein acrylic polymers arepoly(meth)acrylate.
 16. The over-coating agent for forming fine patternsaccording to claim 12, wherein acrylic polymers are poly(meth)acrylate.17. The over-coating agent for forming fine patterns according to claim8 or 9, which is an aqueous solution having a concentration of 3-50mass.
 18. A method of forming fine patterns comprising the steps ofcovering a substrate having thereon photoresist patterns with theover-coating agent for forming fine patterns of any one of claim 1, 8 or9, then applying heat treatment to shrink the applied over-coating agentunder the action of heat so that the spacing between the adjacentphotoresist patterns is lessened, and subsequently completely removingthe applied film of the over-coating agent.
 19. The method of formingfine patterns according to claim 18, wherein the heat treatment isperformed by heating the substrate at a temperature that does not causethermal fluidizing of the photoresist patterns on the substrate.
 20. Theover-coating agent according to claim 5 which contains 0.1 to 15 mass %of the amide group containing monomer in the over-coating agent (assolids).